Page 138 - Accounting Information Systems

CHAPT E R 2 Introduction to Transaction Processing 109

22. BACKUP AND RECOVERY file for a sequential file update process. Indicate the
PROCEDURES FOR DATABASE FILES order in which the transactions are processed. Indicate
which master file records are updated and which are
Figure 2-30 provides a backup and recovery system for
read and written, unchanged, into the new master file.
files that are updated using a destructive update approach.
Also illustrate the relationship between the transaction
Now think about a specific situation that might use this
file and the master file, that is, T ¼ M, T < M, and T >
approach. A company creates its sales order transaction
M, in your answer. How would the update change if a
file in batches. Once a day, a sales clerk compiles a trans-
direct access file is used instead?
action file by entering data from the previous day’s sales
orders to the transaction file. When these transactions
have all been entered and the transaction file passes edit-
PROBLEM 24: CODING SCHEME
ing, the transaction file is used to destructively update
both the sales and the accounts receivable master files.
Transaction Master
Each of these master files is then backed up to a magnetic File File
tape. The magnetic tapes are stored (offline) in a remote Records Records
Order of Order of
location. Now consider what might happen if, in the mid-
Processing Processing
dle of an update of the sales master file, lightning hit the
company’s building, resulting in a power failure that (Key) (Key)
caused the computer to corrupt both the transaction file 1 Data 1 Data
and the master files.
6 2
a. Which, if any, files contain noncorrupted
data (transaction file, accounts receivable 8 3
master file, sales master file, or backup master 9 4
files)?
b. Will a clerk have to re-enter any data? If so, what 10 5
data will have to be re-entered?
13 6
c. What steps will the company have to take to obtain
noncorrupted master files that contain the previous 11 7
day’s sales data?
15 8
23. HASHING ALGORITHM 17 9
The systems programmer uses a hashing algorithm to 10
determine storage addresses. The hashing structure is
9,997/key. The resulting number is then used to locate 11
the record. The first two digits after the decimal point 12
represent the cylinder number, while the second two
digits represent the surface number. The fifth, sixth, and 13
seventh digits after the decimal point represent the 14
record number. This algorithm results in a unique
address 99 percent of the time. What happens the re- 15
mainder of the time when the results of the algorithm 16
are not unique? Explain in detail the storage process
when key value 3 is processed first, key value 2307 at a 17
later date, and shortly thereafter key value 39.
18
24. UPDATE PROCESS 19
Examine the diagram for Problem 24, which contains 20
the processing order for a transaction file and a master